Of the various types of valves utilized for controlling the flow of fluid within conduit systems, rotary plug valves have been found to be quite popular. Rotary plug valves are typically of compact design and are not excessively tall in comparison with many other types of valves having substantially the same flow passage dimension. Where physical size and height is an important or mandatory design consideration, rotary plug valves are widely used. Rotary plug valves are typically of simple nature, utilizing few moving parts and are of nominal cost, and these features substantially enhance the competitive nature of plug valves.
Among the disadvantages of rotary plug valves, however, are the disadvantages of operational pressure range and sealing ability. Most rotary plug valves function properly only at relatively low pressure ranges, for example in the order of 0-150 psig. This operational pressure restriction, in many flow systems, requires that other, less desirable, but higher pressure valves be utilized. Where plug valves incorporate lubricant enhanced sealing, additional sealant must be introduced into the sealant chambers quite often to insure against leakage. This requirement is an expensive service consideration which is frequently detrimental to the employment of such valves. Also, the lubricant sealant must be compatible with the product controlled by the valve.
In many cases, elastomeric sealing material is incorporated in the plug valve mechanism for establishment of the seal between the rotatable plug and the sealing surfaces of the valve body. The elastomeric sealing material tends to wear at a rapid rate, especially in valves of larger size, and therefore presents a problem from the standpoint of servicing, especially if the valve is intended for frequent cycling during use.
To gain the advantages of reasonably high operational pressure and extended service life of sealing material, plug valves have been developed that incorporate mechanically enhanced sealing. In this case, a rotatable plug element having a flow port formed therein is formed to define external interlocking connections and cam surfaces that mate with interlocking connections and cam surfaces defined by a pair of slip elements. The slip elements incorporate sealing elements, typically of the molded elastomeric type, with sealing surfaces defined within the valve body as the slip elements are moved laterally by the interengaging tapered cam surfaces of the plug member and slips. A valve actuator imparts vertical movement to a valve stem and a cam follower of the actuator traverses a typically L-shaped groove to control linear and rotational movement of the valve stem and plug member. Seal life is materially enhanced due to lateral movement of the slips into direct sealing engagement with the seating surfaces of the valve body. High pressure service capability is promoted by cam induced mechanically enhanced sealing.
It has been found, however, that the valve actuator of plug valves having plug and slip assemblies is frequently subjected to unbalanced operational forces and therefore may require frequent servicing due to accellerated wear induced by such forces. Accellerated wear is typically manifested in the plug rotational system of the valve and actuator assembly requiring frequent replacement of valve stems and rotational control elements such as cams and cam follower pins. It is desirable to provide a valve and actuator assembly incorporating a lift-turn type plug and slip system whereby both lifting and turning movements are accomplished by an actuator mechanism, with force transfer from the valve to the actuator being accomplished in evenly distributed manner and thus insuring that valve and actuator components are not susceptible to excessive wear inducing forces.
It is considered desirable to augment the sealing ability of the valve stem packing with a metal-to-metal seal and to provide stop means that limits upward movement of the valve and slip assembly. It is also desirable to provide means for insuring that the force applied by the valve actuator is not transmitted through the stem rotation mechanism of the valve and actuator assembly.
Accordingly, it is a primary feature of the present invention to provide a novel lift-turn type plug valve having a plug and slip assembly in combination with a valve actuator system that is designed for balanced transfer of operational forces from the valve mechanism.
It is also a feature of the present invention to provide a novel lift-turn type plug valve incorporating a valve actuator mechanism having opposed bearing supported cam follower elements that cooperate with cam grooves defined in an actuator stem for efficient force transfer during rotational movement of the plug element.
Among the several features of this invention is contemplated a novel lift-turn type valve mechanism incorporating a cam guided valve actuator mechanism wherein line contact is established between cam follower roller elements and tapered cam surfaces defined by a cam groove, thus preventing overstressing and excessive wear of cam followers or cam surfaces and thus extending the service life of the valve mechanism.
It is also a feature of the present invention to provide a novel lift-turn valve and actuator system wherein bearing supported cam follower elements are supported by a housing structure and are simply and quickly removed and replaced in the event cam follower wear should occur.
Another feature of this invention concerns the use of novel bearing supported cam follower elements that are provided with a lubrication system to insure easy servicing and extended operational service.
It is another feature of this invention to provide a novel valve actuator system for a lift-turn plug valve mechanism wherein an actuator housing is provided that is easily and simply fabricated to insure low cost manufacture that enhances the competitive nature of the valve actuator system.
Another feature of the present invention contemplates the provision of a novel valve actuator system for lift-turn type plug valves wherein a fabricated actuator housing is provided having tubular end sections such as may be formed by common steel pipe with an intermediate portion of the actuator housing defined by a forging for optimum machining capability and for adequate support of roller bearing type cam follower elements.
It is also a feature of the invention to provide a novel lift-turn type valve mechanism wherein a metal-to-metal seal is established between the valve stem and bonnet in the open position of the valve to augment the sealing ability of the stem packing system.
Another feature of the invention concerns the provision of internal stop means that prevents valve actuator forces from being applied to the rotational mechanism of the actuator.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration hereof. The form of the invention which will now be described in detail illustrates the general principles of this invention, but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.